<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../js/vue.js"></script>
</head>

<body>
    <div id="root">
        <h1>今天天气{{info}}</h1>
        <!-- <button @click='this.isHot = !this.isHot'></button> -->
        <button @click="changeWeather">切换天气</button>
    </div>
</body>
<script>
    Vue.config.productionTip = false //组织vue在启动时生成生产提示
    const vm = new Vue({
        el: '#root',
        data: {
            isHot: true
        },
        computed: {
            info() {
                return this.isHot ? '炎热' : '凉爽'
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        //正常写法：
        // watch:{
        //     isHot:{
        //         immediate:true,//初始化时 让handler调用一下
        //         deep:true,//深度监视
        //         handler(newValue,oldValue){
        //             console.log('isHot被修改啦',newValue,oldValue);
        //         }
        //     }
        // }
        //简写：
        // watch:{
        //     isHot:(newValue,oldValue){
        //         console.log('isHot被修改啦',newValue,oldValue,this);
        //     }
        // }
    })
    //正常写法
    vm.$watch('isHot', {
        immediate: true,
        deep:true,
        handler(newValue, oldValue) {
            console.log('isHot被修改啦', newValue, oldValue);
        }
    })
    //简写
    // vm.$watch('isHot',(newValue,oldValue)=>{
    //     console.log('isHot被修改啦',newValue,oldValue,this);
    // })     

</script>

</html>